Avoid heap allocation in SkPictureStateTree constructor

src/core/SkPictureStateTree.cpp

Index: src/core/SkPictureStateTree.cpp
===================================================================
--- src/core/SkPictureStateTree.cpp	(revision 12590)
+++ src/core/SkPictureStateTree.cpp	(working copy)
@@ -11,19 +11,16 @@
 
 SkPictureStateTree::SkPictureStateTree()
     : fAlloc(2048)
-    , fRoot(NULL)
     , fLastRestoredNode(NULL)
     , fStateStack(sizeof(Draw), 16) {
-    SkMatrix* identity = static_cast<SkMatrix*>(fAlloc.allocThrow(sizeof(SkMatrix)));
-    identity->reset();
-    fRoot = static_cast<Node*>(fAlloc.allocThrow(sizeof(Node)));
-    fRoot->fParent = NULL;
-    fRoot->fMatrix = identity;
-    fRoot->fFlags = Node::kSave_Flag;
-    fRoot->fOffset = 0;
-    fRoot->fLevel = 0;
-    fCurrentState.fNode = fRoot;
-    fCurrentState.fMatrix = identity;
+    fRootMatrix.reset();
+    fRoot.fParent = NULL;
+    fRoot.fMatrix = &fRootMatrix;
+    fRoot.fFlags = Node::kSave_Flag;
+    fRoot.fOffset = 0;
+    fRoot.fLevel = 0;
+    fCurrentState.fNode = &fRoot;
+    fCurrentState.fMatrix = &fRootMatrix;
     *static_cast<Draw*>(fStateStack.push_back()) = fCurrentState;
 }
 
@@ -78,7 +75,7 @@
 
 SkPictureStateTree::Iterator SkPictureStateTree::getIterator(const SkTDArray<void*>& draws,
                                                              SkCanvas* canvas) {
-    return Iterator(draws, canvas, fRoot);
+    return Iterator(draws, canvas, &fRoot);
 }
 
 void SkPictureStateTree::appendNode(uint32_t offset) {